1. Technical Field
The invention relates to a flange bearing having a bearing shell and at least one thrust washer, wherein the thrust washer, of which there is at least one, is attached to an outer circumferential surface of the bearing shell.
The invention also relates to a method of producing a flange bearing having a bearing shell and at least one thrust washer, wherein the thrust washer, of which there is at least one, is attached to an outer circumferential surface of the bearing shell.
The invention also relates to a clamping device, in particular a clamping device for performing the above-mentioned production method.
2. Related Art
For the purposes of the present invention, the term “flange bearing” is used as a collective term for flange bearing half shells and bushings, such that the bearing shell may be understood to mean both a bearing half shell and a cylindrical or tubular bushing, wherein the thrust washer is annular or takes the form of a ring segment, corresponding to the bearing shell. If the thrust washer takes the form of a ring, as a rule a continuous ring or an almost continuous ring with one joint is provided.
Such flange bearings are used for numerous applications, in particular for bearing-assisted mounting of heavily loaded, fast-rotating shafts requiring wear-free mounting, such as the crankshaft and/or camshaft of an internal combustion engine. These flange bearings have a bearing shell and at least one thrust washer, which is attached to the left- and/or right-hand edge of the outer circumferential surface of the bearing shell.
The bearing shell serves to absorb radial bearing forces, which are introduced via the shaft rotating in the bearing shell, whereas the rust washer, of which there is at least one, serves to absorb axial forces. If there is a need to absorb axial forces in both directions of the shaft two thrust washers have to be provided, since each thrust washer is in a position only to absorb the forces directed towards its overlay. Cheeks are provided on the shaft, by means of which the shaft is supported on the thrust washer, of which there is at least one.
Due to the right-angle bends in the crankshaft, the bearings for mounting the crankshaft in the crankcase are as a rule divided, wherein in principle continuous bearings and dismantlable crankshafts could also be used.
The flange bearings conventionally used for axial and radial mounting of a crankshaft consist of a semicircular bearing shell and at least one corresponding thrust washer, which is attached to the outer circumferential surface on the end face of the bearing shell to absorb the axial bearing forces. Two such flange bearings make a cranks bearing. They are accommodated in a bearing bore arranged in the crankcase, which bearing bore is likewise divided, each part being semicircular.
In each case, a semicircular bearing shell is accommodated by a corresponding semicircular recess in the so-called bearing saddle or beating cover, wherein, in addition, at least one further recess has to be provided for accommodating and fixing the thrust washer, of which there is at least one.
The requirement to provide recesses for accommodating the thrust washers is a consequence of the fact that the thrust washers are as a rule connected only loosely or non-permanently to the bearing shell or multipart flange bearings are used, in which the bearing shell and at least one thrust washer are mounted separately in the crankcase.
In contrast to the two-part flange bearings for mounting a crankshaft, one-piece flange bearings are conventionally used in internal combustion engines to mount camshafts. These flange bearings comprise a tubular bushing, on the end face of which there is arranged a thrust washer. In principle, the flange bearings have only one thrust washer, since they are press-fitted into the bearing bore accommodating them and thus have to have one side which is accessible and not provided with a thrust washer, thereby allowing such an assembly process. To construct a bearing which may absorb axial forces in both directions of the camshaft, as a rule two bushings are provided for each bearing, wherein one bushing is press-fitted from the left and one from the right into the bearing bore.
DE-OS 25 28 576 discloses a flange bearing which comprises a semicircular bearing shell and a thrust washer connected with said bearing shell. Therein, both the semicircular bearing shell and the thrust washer consist of a backing member and a facing applied to the backing member. The bearing shell backing member is connected to the thrust washer backing member by spot welding at localized points.
One of the backing members preferably comprises radially directed tabs, which form the localized points for the weld joint between the backing members. The tabs are as a rule located on the thrust washer backing member, slots being formed in the bearing shell backing member which each accommodate one tab.
Welding of the tabs introduced into the slots to the end face of the bearing shell forms a rigid connection. The purpose of this connection is primarily to allow simple, preferably mechanized, assembly, whereas such a weld joint does not serve the purpose of ensuring a stable connection between bearing shell and thrust washer during operation of the internal combustion engine.
Since the connection is restricted to localized points, large forces act at these points during operation, which may possibly lead to breakage of the weld points. This is again dealt with in the design of the crankcase by providing recesses on the bearing blocks for accommodating the thrust washers. Should the weld joint then become fatigued during operation, the recess may take over from the weld joint the task of mounting and fixing the thrust washers in the crankcase.
A flange bearing which is very similar to this flange bearing and in which the bearing shell is likewise welded to the trust washers is disclosed in DE 34 25 180 A1.
The thrust washers designated thrust half rings are connected to the bearing shell by projection welding or by capacitor discharge welding. The thrust half rings are made in such a way that the radius of their inner circumference corresponds in a central area to the radius of the outer circumference of the bearing shell. This central area, which serves as an attachment area for the weld joint arrangement, is adjoined to the right and left by lateral areas in which the inner circumference of the thrust half rings has a larger radius than the radius of the outer circumference of the bearing shell.
The half rings preferably comprise protrusions for performing projection welding and the bearing shell preferably comprises countersunk seat areas for accommodation and welding-on of the thrust half rings.
The finished flange bearing has a bearing shell in which the half rings are connected with the end face of the bearing shell by spot welding. However, it has emerged that, during operation of the internal combustion engine, the thrust washers become detached due to the axial forces introduced by the crankshaft. This is accepted, however, since the problem which this flange bearing was developed to solve consisted in providing a bearing shell in which the connection between it and the thrust flanges was sufficiently firm to allow mechanized mounting (c.f. DE 34 25 180 A1, page 5, line 10 ff).
As is the case with the flange bearings of the first-mentioned published patent application, recesses have also to be provided here to accommodate the thrust washers in the bearing blocks of the crankcase. This results in a complex design and cost-intensive manufacture of the crankcase. In addition, the flange bearings welded in accordance with the prior art have to be post-machined, since, as a result of warping caused by weld heat, their thrust washers are not arranged as required, perpendicularly to the bearing shell.
The thrust washers arranged at a slight angle have the consequence that the sliding surface located thereon for absorbing the axial bearing forces and for supporting the crankshaft via the crank cheeks is wise not arranged perpendicularly to the crank axis, but rather at an angle thereto. As a result, the thrust washers are not loaded evenly over their entire sliding surface, but rather only partially, which may lead to overloading, resulting in material abrasion and bearing destruction, and also to vibration breakage of the trust washer.
In addition to the welded flange bearings according to the prior art, in which the weld joint does not as a rule constitute a permanent weld joint, but merely one which simplifies mounting, built-up flange bearings are also a possibility. Such a built-up flange bearing shell is disclosed in DE 199 24 854 C1. With this flange bearing, the semicircular bearing shells comprise retaining recesses in the area of an axial rim portion of the radial bearing part.
The inwardly projecting retaining tongues arranged on the support washer, designated axial bearing part, are introduced into these retaining recesses. At least one of the retaining recesses is open at the edge and has a bendable web, delimiting the recess axially, which is bent round after insertion of the thrust washer into the bearing shell and forms a retaining tongue undercut and thus secures the thrust washer to the bearing shell. However, such interlockingly assembled flange bearings exhibit low dimensional accuracy due both to the relatively loose, interlocking connection and to the deformation to be effected to produce the interlocking connection. Furthermore, effecting an interlocking connection by deforming the components is itself relatively time-consuming and thus expensive.
A flange bearing in which the bearing shell consists of a tubular bushing, to which there is welded by laser welding a circular ring-shaped thrust washer in the form of a flange, is disclosed in DE 198 23 316 A1.
Such bushings are used to bearing-mount camshaft in internal combustion engines. In principle, these flange bearings have only one thrust washer, since they are press-fitted into the bearing bore accommodating them and thus have to have one side which is accessible and not provided with a thrust washer. To construct a beg which may absorb axial forces in both directions of the camshaft as a rule two bushings are provided for each by, wherein one bushing is press-fitted from the left and one from the right into the bearing bore.
The weld joint generated between thrust washer and bushing is a permanent connection, which serves not only as a mounting aid but is also intended, moreover, to ensure fixing of the thrust washer in operation. Consequently, when such bushings are used, no recess has to be provided to accommodate the thrust washer in the bearing.
A disadvantage of the thus constructed flange bearings, produced according to the prior art, is shape inaccuracy, however. Shape inaccuracy is again caused by the heat introduced during the welding process and the thermal stresses resulting during cooling of the assembled flange bearing, which cause the thrust washer on the finished, cooled flange bearing not to stand perpendicular to the axis of the flange bearing, as desired, but to be warped, i.e. during the cooling process the thrust washer tilts away from the perpendicular in the direction of the weld seam. For this reason, the thrust washers have to be thoroughly post-machined, in order to be able to comply with manufacturing tolerances. This increases the number of manufacturing operations and thus the production costs.
Another possibility, which would allow the recesses for accommodating the thrust washers to be dispensed with, is provided by a method by which the flange bearings are made in one piece. This method starts with a specially formed backing member faced with a friction-reducing material. Shaping of the layered backing member to produce a flange bearing with bearing shell and at least one thrust washer requires numerous complex shaping operations, however, which render a flange bearing constructed in one piece in this way an extremely expensive product. Consequently, the one-piece construction of the flange bearing is not expedient either, if it is desired to provide a good value flange bearing in which the bearing shell is connected permanently and stably with the at least one thrust washer.
The prior art expounded demonstrates unequivocally the problems facing the bearing manufacturer who wishes to provide a cost-effective bearing. Flange bearings in which the bearing shell and the thrust washer, of which there is at least one, are not connected at all, or are connected together only loosely (DE 199 248 54 C1) or not permanently (DE 34 25 180 A1), for example by a weld joint serving merely as a mounting aid, require the provision of recesses for accommodating the thrust washer in the bearing block.
Firmly connected, for example built-up flange bearings, as disclosed by DE 19 823 316 A1, are cost-intensive due the relatively complex production process.
All bearings require post-machining after effecting the interlocking or material connection.
Although one-piece flange bearings render unnecessary the recess for accommodating the thrust washer, they are themselves cost-intensive and thus do not provide any real alternative to the flange bearings known from the prior art.
Against this background, it is the object of the invention to provide a flange being having a bearing shell and at least one thrust washer connected to the bearing shell, in which the bearing shell is connected permanently with the at least one thrust washer, thereby rendering dispensable the recess for accommodating the at least one thrust washer to be provided according to the prior art, wherein the flange bearing is intended to provide the best possible value, in particular to do away with post-machining due to an inclined, non-perpendicular thrust washer.
Another sub-object of the present invention is to provide a method of producing a flange bearing having a bearing shell and at least one thrust washer, with which the bearing shell is permanently connected to the thrust washer, thereby rendering dispensable the recesses for accommodating the at least one thrust washer and allowing the most economic production possible of such flange bearings.
Another sub-object of the present invention is to provide a clamping device, in particular a clamping device for performing the above-mentioned production method.